Electronic circuits and circuit boards

ABSTRACT

A method of forming a circuit board includes, a) providing a temporary substrate; b) depositing an uncured electrically insulative circuit board material over the temporary substrate, the circuit board material adhering to the temporary substrate; c) substantially curing the uncured circuit board material into at least one self supporting sheet; d) providing circuit traces atop the cured self supporting sheet; e) mounting an electronic circuit component atop the cured self supporting sheet in electrical communication with the circuit traces; and f) peeling the temporary substrate and cured self supporting sheet from one another. An electronic circuit of the invention includes, i) a self-supporting electrically insulative ink or paint substrate, the ink or paint substrate having an outer surface; ii) circuit traces provided on the ink or paint substrate outer surface; and iii) at least one electronic circuit component mounted to the ink or paint substrate outer surface in electrical connection with the circuit traces.

RELATED PATENT DATA

This patent resulted from a divisional application of U.S. applicationSer. No. 08/585,428, filed on Jan. 11, 1996, entitled "Method of Forminga Circuit Board" listing the inventors as Rickie C. Lake, Joe Mousseauand Mark E. Tuttle.

TECHNICAL FIELD

This invention relates generally to methods of forming circuit boards,and to electronic circuit constructions.

BACKGROUND OF THE INVENTION

Integrated circuits and other components are typically surface mountedto printed wiring boards having conductive traces formed thereon. Theelectronic components might be mounted to one or both sides of suchboards. Such components might constitute single discrete electroniccomponents, such as capacitors and resistors, or constitute fabricatedintegrated circuit device packages.

Printed circuit boards have typically comprised thick, monolithic boardsmade of a ceramic or plastic materials. The materials of constructionare highly electrically insulative, with the surfaces thereof beingprovided with printed circuit traces and landing areas to which thecomponents mount. In certain applications, there is a continuing driveto produce thinner circuit board devices, such as might be receivedwithin a flexible credit card or radio frequency tag device. Such thincircuit board devices are typically encapsulated in an insulative,protecting encapsulating material, such as polyethylene. However,encapsulating materials such as polyethylene do not adhere very well totypical circuit board materials.

This invention concerns improved methods and materials of constructionrelated to printed circuit board fabrication.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a top view of a substrate utilized in forming a circuit boardin accordance with the invention.

FIG. 2 is a view of the FIG. 1 substrate at a processing step subsequentto that shown by FIG. 1.

FIG. 3 is a cross-sectional view of FIG. 2, taken along line 3--3 inFIG. 2.

FIG. 4 is a top view of the FIG. 1 substrate at a processing stepsubsequent to that shown by FIG. 2.

FIG. 5 is a cross-sectional view taken through line 5--5 in FIG. 4.

FIG. 6 is a top view of the FIG. 1 substrate at a processing stepsubsequent to that shown by FIG. 4.

FIG. 7 is a cross-sectional view taken through line 7--7 in FIG. 6.

FIG. 8 is a top view of the FIG. 1 substrate shown at a processing stepsubsequent to that of FIG. 6.

FIG. 9 is a cross-sectional view taken through line 9--9 in FIG. 8.

FIG. 10 is a view of the FIG. 9 fragment shown at a processing stepsubsequent to that depicted by FIG. 9.

FIG. 11 is a cross-sectional view of a circuit board component shown ata processing step subsequent to that depicted by FIG. 10.

FIG. 12 is a view of an alternate embodiment circuit board assembly inan alternate method of forming a circuit board in accordance with theinvention.

FIG. 13 is a view of the FIG. 12 construction at a processing stepsubsequent to that shown by FIG. 12.

FIG. 14 is a top view of another alternately processed substrate and amethod of forming a circuit board in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with one aspect of the invention, a method of forming acircuit board comprises:

providing a temporary substrate;

depositing an uncured electrically insulative circuit board materialover the temporary substrate, the circuit board material adhering to thetemporary substrate;

substantially curing the uncured circuit board material into at leastone self supporting sheet;

providing circuit traces atop the cured self supporting sheet;

mounting an electronic circuit component atop the cured self supportingsheet in electrical communication with the circuit traces; and

peeling the temporary substrate and cured self supporting sheet from oneanother.

In accordance with another aspect of the invention, a method of forminga circuit board comprises:

providing a temporary substrate;

a providing a series of discrete patterns of an uncured electricallyinsulative circuit board material over the temporary substrate, thediscrete patterns forming desired outlines of a plurality of finishedcircuit boards, the circuit board material adhering to the temporarysubstrate;

substantially curing the uncured circuit board material into a pluralityof self supporting circuit board sheets;

providing circuit traces atop the plurality of cured self supportingcircuit board sheets;

mounting electronic circuit components atop the plurality of cured selfsupporting sheets in electrical communication with the circuit traces;and

after providing the circuit traces and mounting the electronic circuitcomponents, peeling the temporary substrate and plurality of cured selfsupporting sheets from one another.

In accordance with still a further aspect of the invention, anelectronic circuit comprising:

a self-supporting electrically insulative ink or paint substrate, theink or paint substrate having an outer surface;

circuit traces provided on the ink or paint substrate outer surface; and

at least one electronic circuit component mounted to the ink or paintsubstrate outer surface in electrical connection with the circuittraces.

More particularly and first with reference with FIG. 1, a thin temporarysubstrate or support film 10 is provided. Preferably, support film 10constitutes a flexible material, although rigid materials such as glass,are also contemplated. Example and preferred other materials forsubstrate 10 include metal foils, metal plates, ceramics, wax orwax-coated substrates, polyester, Teflon®, plastics, and mixturesthereof.

Referring to FIGS. 2 and 3, a series of discrete patterns 12 of anuncured electrically insulative circuit board material is provided overtemporary substrate 10. Discrete patterns 12, as shown, form desiredresultant outlines of a plurality of finished circuit boards. The mostpreferred circuit board material is ink provided to an example thicknessof 0.5 mil to 4 mil. Example inks include PSP™ series inks availablefrom NAZ-DAR Company of Kansas City, Mo. and Chicago, Ill. Such inksconstitute acrylic, ultraviolet light curable inks typically heretoforeonly having been understood to be utilized in the graphic art industry,and never having been understood to be utilized as a self-supportingsubstrate utilized as a circuit board. Other example preferred circuitboard materials in accordance with the invention include epoxies,polyester resins, polyurethanes, paint, varnish and mixtures thereof.

In accordance with the invention, such materials would be deposited orprovided to substrate 10 in an initially uncured state, and yet adheresuitably to substrate 10. The method further comprises substantiallycuring the uncured circuit board material into a plurality of effectiveself-supporting capable circuit board sheets. Such curing will depend onthe type of material utilized as the circuit board material of outlines12. For example, ultraviolet light curable ink would be subjected tocuring by exposing the FIGS. 2 and 3 construction to ultraviolet light.Other materials may require exposure to elevated temperatures for acertain period of time to effect desired curing. Further, othermaterials may inherently cure upon exposure to ambient air over asuitable period of time. The preferred manner by which discrete patterns12 are provided is by a screen printing or stenciling technique.Alternate techniques could, of course, be utilized, but are believed tobe less preferred.

Referring to FIGS. 4 and 5, desired circuit traces are provided atop theplurality of cured self-supporting circuit board sheets 12. Such arepreferably provided by screen printing of a conductive material, such asEMCA-REMEX P2607 polymer silver available from Ablestick Laboratories ofMontgomeryville, Pa.

Referring to FIGS. 6 and 7, a series of electronic circuit components 18are mounted atop the plurality of cured self-supporting sheets 12 inelectrical communication with circuit traces 14, with at least one suchcomponent being shown mounted to each sheet 12. Such components mightcomprise any electronic component for the circuit, such as integratedcircuit packages, capacitors, resistors, transistors, etc. Components 18can be mounted with conductive epoxy, or by other means.

Referring to FIGS. 8 and 9, an electrically insulative encapsulatinglayer 20 is provided over cured circuit board material 12 having circuittraces 14 and electronic circuit components 18 provided thereon. Anexample and preferred or typical encapsulation material is Epoxy ResinR1055 mixed with Hardener H5039 available from Epic Resin, Inc. ofPalmyra, Wis.

Referring to FIG. 10, the encapsulation material is allowed toeffectively cure, and then temporary substrate 10 and a singularcomposite of the collective plurality of circuit board sheets 12 withinmass 20 are peeled away from one another.

Referring to FIG. 11, the resultant stripped composite sheet is cut bycutting through encapsulating layer 20 to form a plurality of discreteencapsulated circuit boards 22 having circuit traces 14 and at least onemounted electronic circuit component 18.

Preferably, the resultant discrete encapsulated circuit boards 22 areprovided to be rigid, although a flexible construction is alsocontemplated thus with the cured circuit board material 12 alsoinherently preferably being flexible in such instance. Such will dependprincipally upon the material of composition of circuit boards 12,material 20 and their respective thicknesses. Further in theabove-described embodiment, preferably the removed temporary substrate10 is reused in fabricating additional circuit boards in accordance withthe invention. Further, each of the temporary substrate, circuit boardmaterial and encapsulating layer can be flexible or rigid, with any ofvarious combinations of the same. Also, the electronic circuit componentare preferably mounted before peeling of the temporary substrate, butmounting after peeling is also contemplated.

Alternate methods and constructions are also contemplated, with theinvention only being limited by the accompanying claims appropriatelyinterpreted in accordance with the Doctrine of Equivalents. By way ofexample only, cutting of discrete encapsulated circuit boards might beconducted before the peeling step, with such cutting also extendingthrough the temporary substrate. Subsequently, the respective temporarycut pieces of substrate would be peeled from the respective compositecircuit boards. This is shown by FIGS. 12 and 13. However in suchinstance, the temporary substrates would not be practically reusable.

Alternately, the uncured printed circuit board material as-depositedmight be blanket deposited over the entirety of surface of temporarysubstrate 10. Subsequent circuit trace patterning and electroniccomponent mounting could occur as described above, with the subsequentcutting step cutting through the encapsulation material as well as thecircuit board material to form the desired finished compositeencapsulated circuit components.

Yet another alternate example is described with reference to FIG. 14.Like numerals from the first described embodiment are utilized whereappropriate, with differences being indicated by the suffix "a" or withdifferent numerals. Here, a series of discrete dams 35 are providedaround the respective cured circuit board sheets 12. Circuit boardtraces 14 and components 18 would be previously provided as in the firstdescribed embodiment. With dams 35 in place, electrically insulativeencapsulating material would be provided within the confines of the damsover the cured circuit board sheets 12 to define a plurality of discreteencapsulated circuit board sheets 22a. Subsequently, temporary substrate10 would be peeled away relative to discrete encapsulated circuit boards22a. Alternately, a spatula could be used. The subject dam materialcould be removed either before or after the peeling step.

Further alternately by way of example only, provision of encapsulatingmaterial might be entirely eliminated in certain desired applications.Regardless, a desired outcome in accordance with the preferredembodiment is the resultant formation of an effective self-supportingflexible or rigid, electrically insulative ink or paint materialsubstrate having circuit traces and at least one electronic componentmounted to an outer surface thereof. Such substrate would subsequentlytypically be mounted to some other construction, such as anothersubstrate, for example a credit card.

The above technology enables the user to employ an extremely thinpermanent substrate for electronic circuitry which in turn minimizesoverall assembly thickness. For example, UV curable inks can be easilyapplied at 1/2 mil thickness (0.0005 inch) onto an easily handled, lowcost, 5 mil thick "releasable" polyester film.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. An electronic circuit comprising:a release layer; anelectrically insulative ink substrate on the release layer and having anouter surface; circuit traces on the ink substrate outer surface; and atleast one electronic circuit component mounted to the ink substrateouter surface in electrical connection with the circuit traces.
 2. Theelectronic circuit of claim 1 further comprising an encapsulatingmaterial encapsulating the substrate outer surface, circuit traces andelectronic component.
 3. The electronic circuit of claim 1 wherein therelease layer is a metal foil.
 4. The electronic circuit of claim 1wherein the release layer is polyester.
 5. An electronic circuitcomprising:a release layer; an electrically insulative paint substrateon the release layer and having an outer surface; circuit traces on thepaint substrate outer surface; and at least one electronic circuitcomponent mounted to the paint substrate outer surface in electricalconnection with the circuit traces.
 6. The electronic circuit of claim 5further comprising an encapsulating material encapsulating the substrateouter surface, circuit traces and electronic component.
 7. Theelectronic circuit of claim 5 wherein the release layer is a metal foil.8. The electronic circuit of claim 5 wherein the release layer ispolyester.
 9. An electronic circuit comprising:a release layer; anelectrically insulative ink substrate on the release layer and having anouter surface; circuit traces on the ink substrate outer surface; and atleast one electronic circuit component mounted to the ink substrateouter surface with conductive epoxy.
 10. The electronic circuit of claim9 wherein the at least one electronic circuit component is in electricalconnection with the circuit traces.
 11. An electronic circuitcomprising:a release layer; an electrically insulative ink substrate onthe release layer and having an outer surface; circuit traces on the inksubstrate outer surface; and at least one electronic circuit componentmounted to the paint substrate outer surface with conductive epoxy. 12.The electronic circuit of claim 11 wherein the at least one electroniccircuit component is in electrical connection with the circuit traces.